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Parsing and serializing XML

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Revision as of 00:08, 14 March 2005
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(added how to serialize XMLHttpRequest objects to files)
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As was previously mentioned, even though <code>[http://xulplanet.com/references/objref/DOMParser.html DOMParser]</code> does have a method named <code>[http://xulplanet.com/references/objref/DOMParser.html#method_parseFromStream parseFromStream()]</code>, it's easier to use [[XMLHttpRequest]]. That's what we'll demonstrate here. As was previously mentioned, even though <code>[http://xulplanet.com/references/objref/DOMParser.html DOMParser]</code> does have a method named <code>[http://xulplanet.com/references/objref/DOMParser.html#method_parseFromStream parseFromStream()]</code>, it's easier to use [[XMLHttpRequest]]. That's what we'll demonstrate here.
-First, read the local or remote XML file into a string: 
<pre> <pre>
var req = new XMLHttpRequest(); var req = new XMLHttpRequest();
-req.open("foo-bar!", "chrome://passwdmaker/content/people.xml", false); +req.open("GET", "chrome://passwdmaker/content/people.xml", false);
req.send(null); req.send(null);
 +alert(req.responseXML.documentElement.nodeName);
</pre> </pre>
-The <code>foo-bar</code> argument of <code>[http://xulplanet.com/references/objref/XMLHttpRequest.html#method_open XMLHttpRequest.open()]</code> specifies the HTTP method to use if the URL (the second argument) is an HTTP(S) URL. Since we're using a <code>chrome://</code> URL, the first argument to <code>[http://xulplanet.com/references/objref/XMLHttpRequest.html#method_open XMLHttpRequest.open()]</code> is ignored. You should change this to an HTTP(S) method (e.g., GET/POST) if using an HTTP(S) URL. 
-Now that we have the XML as a string (in <code>req.responseText</code>), we can use the code similar to that in [[Parsing and serializing XML#Parsing strings into DOM trees|Parsing strings into DOM trees]] to get the XML into a DOM tree:+<code>req.responseXML</code> is the XmlDocument you need.
-<pre>+
-var parser = new DOMParser();+
-var dom = parser.parseFromString(req.responseText, "text/xml");+
-// print the name of the root element+
-dump(dom.documentElement.nodeName);+
-</pre>+
===io.js=== ===io.js===

Revision as of 19:51, 14 March 2005

Mozilla doesn't support the W3C's Document Object Model Load and Save at this moment, so the easiest way to serialize and deserialize DOM trees is to use the following Mozilla-specific interfaces:


Contents

Serializing DOM trees to strings

First, create a DOM tree using code like this.

Now, let's serialize doc — the DOM tree — to a string:

var serializer = new XMLSerializer();
var xml = serializer.serializeToString(doc);

Serializing DOM trees to files

First, create a DOM tree using code like this. If you have already have a DOM tree from using XMLHttpRequest, skip to the end of this section.

Now, let's serialize doc — the DOM tree — to a file (you can read more about using files in Mozilla here):

var serializer = new XMLSerializer();
var foStream = Components.classes["@mozilla.org/network/file-output-stream;1"]
               .createInstance(Components.interfaces.nsIFileOutputStream);
var file = Components.classes["@mozilla.org/file/directory_service;1"]
           .getService(Components.interfaces.nsIProperties)
           .get("ProfD", Components.interfaces.nsIFile); // get profile folder
file.append("extensions");   // extensions sub-directory
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");   // GUID of your extension
file.append("myXMLFile.xml");   // filename
foStream.init(file, 0x02 | 0x08 | 0x20, 0664, 0);   // write, create, truncate
serializer.serializeToFile(doc, foStream, "IS0-8859-1");   // rememeber, doc is the DOM tree
foStream.close();

If you have already have a DOM tree from using XMLHttpRequest, use the same code as above but replace serializer.serializeToFile(doc, foStream, "IS0-8859-1") with serializer.serializeToFile(xmlHttpRequest.responseText, foStream, "IS0-8859-1") where xmlHttpRequest is an instance of XMLHttpRequest.

Parsing strings into DOM trees

var theString='<a id="a"><b id="b">hey!</b></a>';
var parser = new DOMParser();
var dom = parser.parseFromString(theString, "text/xml");
// print the name of the root element
dump(dom.documentElement.nodeName);

Parsing files into DOM trees

XMLHttpRequest

As was previously mentioned, even though DOMParser does have a method named parseFromStream(), it's easier to use XMLHttpRequest. That's what we'll demonstrate here.

var req = new XMLHttpRequest();
req.open("GET", "chrome://passwdmaker/content/people.xml", false); 
req.send(null);
alert(req.responseXML.documentElement.nodeName);

req.responseXML is the XmlDocument you need.

io.js

If you prefer io.js, this code will also parse a file into a DOM tree. Unlike XMLHttpRequest, it will not work with remote files:

var file = DirIO.get("ProfD"); // %Profile% dir
file.append("extensions");
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");
file.append("people.xml");
var fileContents = FileIO.read(file);
var domParser = new DOMParser();
var doc = domParser.parseFromString(fileContents);
// print the name of the root element
dump(doc.documentElement.nodeName);